Conventional fuel cell stacks are described, for example, in Patent Document 1. The fuel cell stack of Patent Document 1 has a stacked cell structure in which assemblies with a reinforcing frame in the outer periphery of an electrolyte (electrolyte membrane) and separators with gas channels formed thereon are stacked. In the fuel cell stack, the separators are disposed inside the reinforcing frames such that the separators do not interfere with the reinforcing frames or that the outer peripheries of the separators are flush with the inner peripheries of the reinforcing frames. The fuel cell stack can maintain its power generation efficiency since deformation of the electrolytes is prevented.